(1) Field of the Invention
The present invention relates to an aromatic polyamide composition. More particularly, it relates to an aromatic polyamide compostion having incorporated therein a solubilizing aid and an amide solvent. This aromatic polyamide composition exhibits good thermal stability and is useful for melt shaping. The present invention also relates to a process for preparing a film from the aromatic polyamide composition.
(2) Description of the Prior Art
Aromatic polyamides possess good thermal resistance, and hence, in recent years, they have been widely used as apparel materials, electrical insulants and other industrial materials in the form of fibers, films, paper and other shaped articles. It is, however, difficult or even impossible to make shaped articles from aromatic polyamides by a melt shaping procedure. This is because aromatic polyamides generally possess very high melting points and the melting points are in a close vicinity to their thermal decomposition points. Thus, conventional aromatic polyamide shaped articles are made by a wet- or dry-shaping procedure wherein the polymer is dissolved in an organic polar solvent such as dimethylformamide, N-methyl-2-pyrrolidone or dimethylacetamide, and the obtained polymer dope is extruded through a nozzle or die into a liquid or gas atmosphere followed by the removal of the solvent from the extrudate. The wet- or dry-shaping procedure is not advantageous in that, first, a large amount of an organic polar solvent is needed for the preparation of the polymer dope, and secondly, a large amount of another organic solvent must be used for the recovery of the organic polar solvent used.
Attempts have been heretofore made wherein an aromatic polyamide is dissolved in a relatively small amount of an organic polar solvent and the obtained polymer dope of a high concentration is extruded at a relatively high temperature. However, as far as poly-m-phenyleneisophthalamide is concerned, these attempts were not successful. This is because poly-m-phenyleneisophthalamide exhibits a marked tendency of being crystallized and insolubilized at a high concentration and a high temperature.
It also has been proposed as disclosed in Japanese Laid-open Patent Applications Nos. 13,543/1977, 15,675/1977, 53,068/1977, 98,764/1977 and 101,298/1977 that poly-m-phenyleneisophthalamide or a copolyamide mainly comprised of m-phenyleneisophthalamide units be dissolved in an excess of an organic polar solvent such as N-methyl-2-pyrrolidone, hexamethylphosphoramide, 2-pyrrolidone or .epsilon.-caprolactam, and then, the obtained solution is heated under vacuum to remove a substantial part of the solvent therefrom. The resultant product is a crystalline polymeric complex possessing a relatively low melting point, which complex is melt-shapable. This proposed process is still not satisfactory. That is, first, a very large amount of the organic polar solvent must be used for the preparation of the polymer solution and a substantial part of the solvent, which has generally a relatively high boiling point, must be evaporated from the prepared polymer solution requiring a large heat energy. Secondly, the crystalline polymeric complex is poor in thermal stability and hence, the melt-shaping thereof must be conducted at a relatively low temperature and completed within a relatively short period of time.